Transformer

ABSTRACT

In a transformer, forward and reverse secondary coils are connected to a single reference electrode or any of a plurality of reference electrodes. The forward secondary coil includes first and second winding portions wound around a forward iron core. The reverse secondary coil includes third and fourth winding portions wound around a reverse iron core. A first primary coil is formed around the first and third winding portions. The second primary coil is formed around the second and fourth winding portions. The single reference electrode or each of the plurality of reference electrodes is in the form of a plate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority on and the benefit of PatentApplication No. 2021-030544 filed in JAPAN on Feb. 26, 2021. The entiredisclosures of this Japanese Patent Application are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present specification discloses a transformer. In particular, thepresent invention relates to a current-doubler transformer.

Description of the Related Art

In recent years, current-doubler transformers have been used as DC-DCconverters or AC-DC converters. Such a transformer includes twosecondary coils that output voltages inverse to each other according tochanges in the input voltage applied to a primary coil. One of thesecondary coils is herein referred to as “forward secondary coil”, andthe other secondary coil is herein referred to as “reverse secondarycoil”. For example, when the output of the forward secondary coil is apositive voltage, the output of the reverse secondary coil is a negativevoltage. The respective outputs of the secondary coils are connected torectifying elements such as diodes, and these rectifying elements areconnected to an output terminal. Thus, for example, the output of theforward secondary coil is output through the output terminal, and thereverse secondary coil is isolated from the output terminal.

In the transformer, when one of the secondary coils is isolated from theoutput terminal, energy is stored in the one secondary coil during theperiod of isolation. In the example mentioned above, energy is stored inthe reverse secondary coil. Once the output voltage of the reversesecondary coil becomes a positive voltage in response to a change in theinput voltage applied to the primary coil, the voltage from the reversesecondary coil is output through the output terminal. In this situation,the output current is high due to the energy arising from an inducedelectromotive force and the stored energy. A study about current-doublertransformers is disclosed in “A Novel Integrated Current DoublerRectifier”, APEC 2000, Fifteenth Annual IEEE Applied Power ElectronicsConference and Exposition.

Current-doubler transformers generate a large amount of heat because ofhigh currents flowing through the transformers. Equipping the housingsof the transformers with additional means such as radiating fins toreduce the temperature rise induced by the heat generation leads toincreases in size and cost of the transformers. There is a demand for atransformer in which heat generation-induced temperature rise is reducedby a simple configuration.

The present inventors aim to provide a current-doubler transformer inwhich heat generation-induced temperature rise is reduced by a simpleconfiguration.

SUMMARY OF THE INVENTION

A preferred transformer includes: a positive-side input electrode; anegative-side input electrode; an output electrode; a single referenceelectrode or a plurality of reference electrodes; a forward iron core; areverse iron core; a first primary coil; a second primary coil; aforward secondary coil; a reverse secondary coil; a first rectifyingelement; and a second rectifying element. A first terminal of the firstprimary coil is connected to the positive-side input electrode, and asecond terminal of the first primary coil is connected to thenegative-side input electrode. A first terminal of the second primarycoil is connected to the positive-side input electrode, and a secondterminal of the second primary coil is connected to the negative-sideinput electrode. A first terminal of the forward secondary coil isconnected to a first terminal of the first rectifying element, and asecond terminal of the forward secondary coil is connected to the singlereference electrode or any of the plurality of reference electrodes. Afirst terminal of the reverse secondary coil is connected to a firstterminal of the second rectifying element, and a second terminal of thereverse secondary coil is connected to the single reference electrode orany of the plurality of reference electrodes. Second terminals of thefirst and second rectifying elements are connected to the outputelectrode. The forward secondary coil includes first and second windingportions both of which are wound around the forward iron core. Thereverse secondary coil includes third and fourth winding portions bothof which are wound around the reverse iron core. The first primary coilis formed around the first and third winding portions. The secondprimary coil is formed around the second and fourth winding portions.The single reference electrode or each of the plurality of referenceelectrodes is in the form of a plate. Winding directions of the firstand second primary coils and the first, second, third, and fourthwinding portions are defined so that voltages inverse to each other aregenerated at the respective first terminals of the forward and reversesecondary coils upon a change in a voltage applied between thepositive-side and negative-side input electrodes. The voltage of thefirst terminal of the forward or reverse secondary coil is outputthrough the output electrode by bringing one of the first and secondrectifying elements into a conducting state while bringing the other ofthe first and second rectifying elements into a non-conducting state.

The transformer includes the forward secondary coil, the reversesecondary coil, the forward iron core around which the forward secondarycoil is wound, the reverse iron core around which the reverse secondarycoil is wound, and the single reference electrode or the plurality ofreference electrodes. The single reference electrode or each of theplurality of reference electrodes is in the form of a plate. In such areference electrode, the cross-sectional area contributing to thermalconduction and the surface area contributing to heat release can easilybe increased. The reference electrode effectively discharges heatgenerated in the secondary coils and iron cores. In the transformer,heat generation-induced temperature rise is reduced by a simpleconfiguration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a transformer according to oneembodiment.

FIG. 2 is a plan view showing the transformer of FIG. 1 with a topcover, a bottom cover, and joints removed.

FIG. 3 is an equivalent circuit diagram of the transformer of FIG. 1.

FIG. 4A is a perspective view showing an iron core of the transformer ofFIG. 1, and FIG. 4B is an exploded view showing the iron cone.

FIG. 5 is a perspective view showing secondary coils of the transformerof FIG. 1.

FIG. 6 is a perspective view showing the secondary coils, iron cores,and a reference electrode of the transformer of FIG. 1.

FIG. 7 is a plan view of the secondary coils, iron cores, and referenceelectrode of FIG. 6.

FIG. 8 is a perspective view showing the reference electrode of thetransformer of FIG. 1.

FIG. 9A is a perspective view showing a primary coil of the transformerof FIG. 1, and FIG. 9B is a cross-sectional view taken along the lineIXb-IXb of FIG. 9A.

FIG. 10 is a perspective view showing the top cover, bottom cover, andjoints of the transformer of FIG. 1.

FIG. 11 is a plan view showing secondary coils according to anotherembodiment.

FIG. 12 is a perspective view showing iron cores, primary coils,secondary coils, and reference electrodes of a transformer according toyet another embodiment.

FIG. 13 is a plan view showing the secondary coils and referenceelectrodes of the transformer of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention based onpreferred embodiments with appropriate reference to the drawings.

FIG. 1 is a perspective view showing a transformer 2 according to oneembodiment. In FIG. 1, the arrow X represents the frontward directionwith respect to the transformer 2, and the opposite direction is thebackward direction with respect to the transformer 2. The arrow Yrepresents the rightward direction with respect to the transformer 2,and the opposite direction is the leftward direction with respect to thetransformer 2. The arrow Z represents the upward direction with respectto the transformer 2, and the opposite direction is the downwarddirection with respect to the transformer 2. The transformer 2 includesa top cover 4, a bottom cover 6, joints 8, iron cores 10, primary coils12, and secondary coils 14. FIG. 2 is a plan view showing thetransformer 2 of FIG. 1 with the top cover 4, bottom cover 6, and joints8 removed. The transformer 2 further includes a reference electrode 16.

As shown in FIGS. 1 and 2, the transformer 2 includes two iron cores 10,two secondary coils 14, and two primary coils 12. As described later,the output voltage of one of the secondary coils 14 and the outputvoltage of the other secondary coil 14 are inverse to each other. Thus,in this specification, one of the two secondary coils 14 is referred toas “forward secondary coil 14 f”, and the other secondary coil 14 isreferred to as “reverse secondary coil 14 r”. Either of the twosecondary coils 14 may be referred to as “forward secondary coil”,although in this embodiment the right secondary coil 14 in FIGS. 1 and 2is referred to as “forward secondary coil”. The iron core 10 aroundwhich the forward secondary coil 14 f is wound is referred to as“forward iron core 10 f”, and the iron core 10 around which the reversesecondary coil 14 r is wound is referred to as “reverse iron core 10 r”.One of the two primary coils 12 is referred to as “first primary coil 12a”, and the other primary coil 12 is referred to as “second primary coil12 b”.

FIG. 3 shows an equivalent circuit of the transformer 2 of FIG. 1.Although not shown in FIGS. 1 and 2, the transformer 2 further includesa positive-side input electrode 18, a negative-side input electrode 20,a first rectifying element 22, a second rectifying element 24, and anoutput electrode 26. The top cover 4, bottom cover 6, and joints 8 arenot illustrated in the circuit diagram of FIG. 3. The following are alsoshown in the circuit diagram of FIG. 3: an AC power supply 25 connectedto the positive-side and negative-side input electrodes 18 and 20 of thetransformer 2; and a capacitor 30 and load 32 that are connected to theoutput electrode 26 and reference electrode 16 of the transformer 2.

FIG. 4A is a perspective view showing the forward iron core 10 f ofFIG. 1. The forward iron core 10 f is in the form of a frame havingouter and inner peripheral surfaces with rectangular contours. Thus, theforward iron core 10 f includes opposing first and second pillarportions 34 and 36 extending parallel to each other and opposing thirdand fourth pillar portions 40 and 42 extending parallel to each otherand perpendicular to the first and second pillar portions 34 and 36.

As shown in FIG. 4B, the forward iron core 10 f is formed of halfframe-shaped first and second halves 44 and 46 combined with each other.There are gaps between the first and second halves 44 and 46. In otherwords, the forward iron core 10 f includes two cut portions 48. In thisembodiment, one of the cut portions 48 is located in the first pillarportion 34, and the other cut portion 48 is located in the second pillarportion 36. The forward iron core 10 f is made of a magnetic material.Typically, the forward iron core 10 f is made of ferrite. The forwardiron core 10 f may be made of an amorphous magnetic material or siliconsteel.

The reverse iron core 10 r has the same structure as the forward ironcore 10 f. That is, the reverse iron core 10 r is in the form of a framehaving outer and inner peripheral surfaces with rectangular contours.Thus, the reverse iron core 10 r includes opposing first and secondpillar portions 50 and 52 extending parallel to each other and opposingthird and fourth pillar portions 54 and 56 extending parallel to eachother and perpendicular to the first and second pillar portions 50 and52 (see FIG. 6 described later). Although not shown, the reverse ironcore 10 r is formed of half frame-shaped first and second halvescombined with each other. There are gaps between the first and secondhalves. The reverse iron core 10 r includes two cut portions. In thisembodiment, one of the cut portions is located in the first pillarportion 50, and the other cut portion is located in the second pillarportion 52. The reverse iron core 10 r is made of a magnetic material.Typically, the reverse iron core 10 r is made of ferrite. The reverseiron core 10 r may be made of an amorphous magnetic material or siliconsteel. As shown in FIG. 2, the forward and revers iron cores 10 f and 10r are arranged side by side. When viewed in plan, the reverse iron core10 r is parallel to the forward iron core 10 f.

FIG. 5 is a perspective view showing the forward and reverse secondarycoils 14 f and 14 r. FIG. 6 is a perspective view showing the forwardand reverse secondary coils 14 f and 14 r combined with the forward andreverse iron cores 10 f and 10 r. FIG. 7 is a plan view of the forwardand reverse secondary coils 14 f and 14 r and forward and reverse ironcores 10 f and 10 r shown in FIG. 6. The reference electrode 16 is alsoshown in FIGS. 6 and 7.

The forward secondary coil 14 f is made of an electrically conductivematerial (conductor). The forward secondary coil 14 f is typically madeof a copper alloy or an aluminum alloy. As shown in FIG. 5, the forwardsecondary coil 14 f includes a first winding portion 58, a secondwinding portion 60, a connection portion 62, a first terminal 64, and asecond terminal 66. Each of the first and second winding portions 58 and60 is a wound conductor in the form of a plate. As shown in FIGS. 6 and7, the first winding portion 58 is wound around the first pillar portion34 of the forward iron core 10 f. The first winding portion 58 coversthe cut portion 48 of the first pillar portion 34. The second windingportion 60 is wound around the second pillar portion 36 of the forwardiron core 10 f. The second winding portion 60 covers the cut portion 48of the second pillar portion 36. In the present specification, being“electrically conductive” means having an electrical resistivity of1.0×10⁻⁵ Ω/m or less.

In this embodiment, there are gaps between the forward iron core 10 fand first winding portion 58 and between the forward iron core 10 f andsecond winding portion 60. Although not shown, a thermally conductiveinsulator may be located on the first pillar portion 34 and between thefirst winding portion 58 and the outer or inner peripheral surface ofthe forward iron core 10 f. That is, the first winding portion 58 may bein indirect contact with the outer or inner peripheral surface of theforward iron core 10 f at the first pillar portion 34 via the thermallyconductive insulator. A thermally conductive insulator may be located onthe second pillar portion 36 and between the second winding portion 60and the outer or inner peripheral surface of the forward iron core 10 f.That is, the second winding portion 60 may be in indirect contact withthe outer or inner peripheral surface of the forward iron core 10 f atthe second pillar portion 36 via the thermally conductive insulator. Inthe present specification, being “thermally conductive” means having athermal conductivity of 1.0 W/m·K or more.

The connection portion 62 connects the first and second winding portions58 and 60. The connection portion 62 extends parallel to the third andfourth pillar portions 40 and 42 of the forward iron core 10 f. Thefirst terminal 64 is in the form of a plate. The first terminal 64projects ahead of the second winding portion 60. The second terminal 66is in the form of a plate. The second terminal 66 is located between thefirst and second winding portions 58 and 60. The second terminal 66,first winding portion 58, connection portion 62, second winding portion60, and first terminal 64 are connected in series in this order.

As shown in FIGS. 5 and 7, the first and second winding portions 58 and60 are wound in opposite directions. Since the first and second pillarportions 34 and 36 are opposed to each other, the magnetic fluxes in thefirst and second pillar portions 34 and 36 flow in opposite directions.Thus, the induced electromotive forces occurring in the first and secondwinding portions 58 and 60 in response to changes in the magnetic fluxesin the forward iron core 10 f act in the same direction. The voltagegenerated between the first and second terminals 64 and 66 of theforward secondary coil 14 f due to the induced electromotive forces isthe sum of the voltage generated in the first winding portion 58 and thevoltage generated in the second winding portion 60. Thus, in the circuitdiagram of FIG. 3, the forward secondary coil 14 f is depicted as havinga structure in which the coil corresponding to the first winding portion58 and the coil corresponding to the second winding portion 60 areconnected in series.

The reverse secondary coil 14 r is made of a conductor. The reversesecondary coil 14 r is typically made of a copper alloy or an aluminum.As shown in FIG. 5, the reverse secondary coil 14 r includes a thirdwinding portion 68, a fourth winding portion 70, a connection portion72, a first terminal 74, and a second terminal 76. Each of the third andfourth winding portions 68 and 70 is a wound conductor in the form of aplate. As shown in FIGS. 6 and 7, the third winding portion 68 is woundaround the first pillar portion 50 of the reverse iron core 10 r. Thethird winding portion 68 covers the cut portion of the first pillarportion 50. The fourth winding portion 70 is wound around the secondpillar portion 52 of the reverse iron core 10 r. The fourth windingportion 70 covers the cut portion of the second pillar portion 52.

In this embodiment, there are gaps between the reverse iron core 10 rand third winding portion 68 and between the reverse iron core 10 r andfourth winding portion 70. Although not shown, a thermally conductiveinsulator may be located on the first pillar portion 50 and between thethird winding portion 68 and the outer or inner peripheral surface ofthe reverse iron core 10 r. That is, the third winding portion 68 may bein indirect contact with the outer or inner peripheral surface of thereverse secondary coil 14 r at the first pillar portion 50 via thethermally conductive insulator. A thermally conductive insulator may belocated on the second pillar portion 52 and between the fourth windingportion 70 and the outer or inner peripheral surface of the reverse ironcore 10 r. That is, the fourth winding portion 70 may be in indirectcontact with the outer or inner peripheral surface of the reverse ironcore 10 r at the second pillar portion 52 via the thermally conductiveinsulator.

The connection portion 72 connects the third and fourth winding portions68 and 70. The connection portion 72 extends parallel to the third andfourth pillar portions 54 and 56 of the reverse iron core 10 r. Thefirst terminal 74 is in the form of a plate. The first terminal 74projects ahead of the fourth winding portion 70. The second terminal 76is in the form of a plate. The second terminal 76 is located between thethird and fourth winding portions 68 and 70. The second terminal 76,third winding portion 68, connection portion 72, fourth winding portion70, and first terminal 74 are connected in series in this order.

As shown in FIGS. 5 and 7, the third and fourth winding portions 68 and70 are wound in opposite directions. Since the first and second pillarportions 50 and 52 are opposed to each other, the magnetic fluxes in thefirst and second pillar portions 50 and 52 flow in opposite directions.Thus, the induced electromotive forces occurring in the third and fourthwinding portions 68 and 70 in response to changes in the magnetic fluxesin the reverse iron core 10 r act in the same direction. The voltagegenerated between the first and second terminals 74 and 76 of thereverse secondary coil 14 r due to the induced electromotive forces isthe sum of the voltage generated in the third winding portion 68 and thevoltage generated in the fourth winding portion 70. Thus, in the circuitdiagram of FIG. 3, the reverse secondary coil 14 r is depicted as havinga structure in which the coil corresponding to the third winding portion68 and the coil corresponding to the fourth winding portion 70 areconnected in series.

As shown in FIGS. 6 and 7, the reverse secondary coil 14 r is shapedsuch that when viewed in plan, the forward and reverse secondary coils14 f and 14 r are symmetrical about a line extending in the front-backdirection and bisecting the distance between the forward and reversesecondary coils 14 f and 14 r. That is, the first and third windingportions 58 and 68 are wound in opposite directions. The second andfourth winding portions 60 and 70 are wound in opposite directions.

FIG. 8 is a perspective view showing the reference electrode 16. Thereference electrode 16 is made of a conductor. The reference electrode16 is typically made of a copper alloy or an aluminum alloy. Thereference electrode 16 is generally in the form of a plate. As shown inFIGS. 6 and 7, the reference electrode 16 is located between the forwardand reverse secondary coils 14 f and 14 r when viewed in plan. Thereference electrode 16 is located between the forward and reverse ironcores 10 f and 10 r when viewed in plan. As shown in FIG. 8, thereference electrode 16 includes a base portion 78, a first extractionportion 80, a second extraction portion 82, a first side portion 84, anda second side portion 86.

As shown in FIGS. 6 and 7, the base portion 78 is located between theforward and reverse iron cores 10 f and 10 r and extends in thefront-back direction. The base portion 78 extends along the fourthpillar portions 42 and 56 of the forward and reverse iron cores 10 f and10 r. The base portion 78 includes a projecting portion 88 projectingoutward from the space between the forward and reverse iron cores 10 fand 10 r. The base portion 78 is buried in the bottom cover 6. Thus, thebase portion 78 is not seen in FIG. 1. The base portion 78 is in directcontact with the bottom cover 6. A thermally conductive insulator may beinterposed between the base portion 78 and bottom cover 6. The baseportion 78 may be in indirect contact with the bottom cover 6, with theinsulator interposed therebetween.

The first and second extraction portions 80 and 82 and the first andsecond side portions 84 and 86 project upward from the bottom cover 6.The first extraction portion 80 extends from the base portion 78 towardthe forward secondary coil 14 f. The first extraction portion 80 is incontact with the second terminal 66 of the forward secondary coil 14 f.Thus, as shown in the circuit diagram of FIG. 3, the forward secondarycoil 14 f is connected to the reference electrode 16. The secondextraction portion 82 extends from the base portion 78 toward thereverse secondary coil 14 r. The second extraction portion 82 is incontact with the second terminal 76 of the reverse secondary coil 14 r.Thus, as shown in the circuit diagram of FIG. 3, the reverse secondarycoil 14 r is connected to the reference electrode 16. The first sideportion 84 extends upward from the base portion 78. As shown in FIG. 6,the first side portion 84 extends along the second pillar portion 36 ofthe forward iron core 10 f. Although not seen in FIG. 6, the second sideportion 86 extends along the second pillar portion 52 of the reverseiron core 10 r.

FIG. 9A is a perspective view showing the first primary coil 12 a. FIG.9B is a cross-sectional view taken along the line IXb-IXb of FIG. 9A.The first primary coil 12 a includes a bobbin 90 and a wire 92. Althoughnot shown, the first primary coil 12 a further includes a first terminalconnected to one end of the wire 92 and a second terminal connected tothe other end of the wire 92. The bobbin 90 is in the form of a frame.The wire 92 is wound in a plurality of turns around the outer peripheryof the bobbin 90. FIG. 9B shows a cross-section of the bobbin 90 and across-section of the wire 92 wound around the bobbin 90. A typicalmaterial of the wire 92 is copper (Cu).

The second primary coil 12 b, like the first primary coil 12 a, includesa bobbin, a wire, a first terminal, and a second terminal. The bobbin ofthe second primary coil 12 b has the same structure as the bobbin 90 ofthe first primary coil 12 a. The wire is wound in a plurality of turnsaround the outer periphery of the bobbin. In this embodiment, the wireof the second primary coil 12 b is wound in a direction opposite to thatin which the wire 92 of the first primary coil 12 a is wound.

In the transformer 2, as shown in FIGS. 1 and 2, the first and thirdwinding portions 58 and 68 are arranged side by side. The frame-shapedfirst primary coil 12 a is disposed to surround the first and thirdwinding portions 58 and 68. In other words, the first primary coil 12 ais formed around the first and third winding portions 58 and 68.

In FIG. 9, the double-headed arrow C1 represents the width of the firstprimary coil 12 a. In FIG. 5, the double-headed arrow W1 represents thewidth of the first winding portion 58, and the double-headed arrow W3represents the width of the third winding portion 68. The width C1 ofthe first primary coil 12 a is similar to the widths W1 and W3 of thefirst and third winding portions 58 and 68. The first primary coil 12 ais wound outside the first winding portion 58 over substantially theentire width of the first winding portion 58. The first primary coil 12a is wound outside the third winding portion 68 over substantially theentire width of the third winding portion 68. In the presentspecification, the statement that “two widths are similar” means thatthe ratio between the two widths is from 0.80 to 1.25.

In the transformer 2, as shown in FIGS. 1 and 2, the second and fourthwinding portions 60 and 70 are arranged side by side. The frame-shapedsecond primary coil 12 b is disposed to surround the second and fourthwinding portions 60 and 70. In other words, the second primary coil 12 bis formed around the second and fourth winding portions 60 and 70.

In FIG. 5, the double-headed arrow W2 represents the width of the secondwinding portion 60, and the double-headed arrow W4 represents the widthof the fourth winding portion 70. The width of the second primary coil12 b is similar to the widths W2 and W4 of the second and fourth windingportions 60 and 70. The second primary coil 12 b is wound outside thesecond winding portion 60 over substantially the entire width of thesecond winding portion 60. The second primary coil 12 b is wound outsidethe fourth winding portion 70 over substantially the entire width of thefourth winding portion 70.

In the circuit diagram of FIG. 3, the first primary coil 12 a isdepicted as having a structure in which the coil wound around theforward iron core 10 f and the coil wound around the reverse iron core10 r are connected in parallel. The depicted structure is logicallyequivalent to that described by stating that “the first primary coil 12a is wound outside the first and third winding portions 58 and 60”. Thesecond primary coil 12 b is depicted as having a structure in which thecoil wound around the forward iron core 10 f and the coil wound aroundthe reverse iron core 10 r are connected in parallel. The depictedstructure is logically equivalent to that described by stating that “thesecond primary coil 12 b is wound outside the second and fourth windingportions 60 and 70”.

As shown in FIG. 3, the first terminal of the first primary coil 12 a isconnected to the positive-side input electrode 18, and the secondterminal of the first primary coil 12 a is connected to thenegative-side input electrode 20. The first terminal of the secondprimary coil 12 b is connected to the positive-side input electrode 18,and the second terminal of the second primary coil 12 b is connected tothe negative-side input electrode 20. The manner of connection of thefirst and second primary coils 12 a and 12 b to the positive-side andnegative-side input electrodes 18 and 20 is defined so that a change inthe voltage between the positive-side and negative-side input electrodes18 and 20 causes the first and second primary coils 12 a and 12 b togenerate magnetic fields acting in the same direction in the forwardiron core 10 f. The manner of connection of the first and second primarycoils 12 a and 12 b to the positive-side and negative-side inputelectrodes 18 and 20 is defined so that a change in the voltage betweenthe positive-side and negative-side input electrodes 18 and 20 causesthe first and second primary coils 12 a and 12 b to generate magneticfields acting in the same direction in the reverse iron core 10 r. Upona change in the voltage between the positive-side and negative-sideinput electrodes 18 and 20, magnetic fields acting in the same directionare generated in the forward and reverse iron cores 10 f and 10 r (forexample, clockwise magnetic fields are generated in the iron cores 10 fand 10 r as viewed from the right in FIG. 1).

As shown in FIG. 3, the first terminal of the first rectifying element22 is connected to the first terminal 64 of the forward secondary coil14 f. The first terminal of the second rectifying element 24 isconnected to the first terminal 74 of the reverse secondary coil 14 r.The second terminals of the first and second rectifying elements 22 and24 are both connected to the output electrode 26. In this embodiment,both the first and second rectifying elements 22 and 24 are diodes. Therectifying elements may be switching elements such as MOSFETs. In thiscase, one of the two switching elements is in the conducting state,while the other switching element is in the non-conducting state. Theswitching elements are switchable between the conducting andnon-conducting states. As previously stated, the first and secondrectifying elements 22 and 24 and the output electrode 26 are notillustrated in FIG. 1.

The top cover 4 covers the two iron cores 10, two secondary coils 14,and two primary coils 12 from above. The top cover 4 is made of anon-magnetic, thermally conductive metal or non-magnetic, thermallyconductive ceramic. Preferred examples of the material of the top cover4 include aluminum alloys, alumina, and magnesium oxide. The top cover 4may contain a cooling liquid therein. A typical example of the coolingliquid is water.

On the bottom cover 6 are mounted the two iron cores 10, two secondarycoils 14, and two primary coils 12. As previously stated, the baseportion 78 of the reference electrode 16 is buried in the bottom cover6. The bottom cover 6 is made of a thermally conductive material. Inthis embodiment, the bottom cover 6 is electrically conductive andconnected to the reference electrode 16. Preferred examples of thematerial of the bottom cover 6 include aluminum alloys. The bottom cover6 may be made of an insulating material. The bottom cover 6 may containa cooling liquid therein. A typical example of the cooling liquid iswater.

FIG. 10 shows the top cover 4, bottom cover 6, and joints 8. There aretwo joints 8 in this embodiment. The joints 8 are located between thetop and bottom covers 4 and 6. The joints 8 connect the top and bottomcovers 4 and 6. The joints 8 are made of a non-magnetic, thermallyconductive metal or non-magnetic, thermally conductive ceramic.Preferred examples of the material of the joints 8 include aluminumalloys, alumina, and magnesium oxide. The joints 8 may contain a coolingliquid therein. A typical example of the cooling liquid is water.

The following will describe the operation of the transformer 2.

In this embodiment, as shown in FIG. 3, the AC power supply 25 isconnected between the positive-side and negative-side input electrodes18 and 20 of the transformer 2. For example, in case that the voltage ofthe positive-side input electrode 18 changes and becomes higher than thevoltage of the negative-side input electrode 20, the amounts of thecurrents flowing through the first and second primary coils 12 a and 12b change, and this leads to changes in the magnetic fluxes in theforward and reverse iron cores 10 f and 10 r. Induced electromotiveforces are accordingly generated in the forward and reverse secondarycoils 14 f and 14 r. Since the forward and reverse secondary coils 14 fand 14 r are wound in opposite directions, voltages acting in oppositedirections are generated in the forward and reverse secondary coils 14 fand 14 r. A forward voltage is applied to one of the first and secondrectifying elements 22 and 24, and a reverse voltage is applied to theother of the first and second rectifying elements 22 and 24. Thus, forexample, the first rectifying element 22 is brought into the conductingstate, while the second rectifying element 24 is brought into thenon-conducting state. The output voltage of the forward secondary coil14 f appears at the output electrode 26. The reverse secondary coil 141is isolated from the output electrode 26, and energy arising from theinduced electromotive force is stored in the reverse secondary coil 14r.

In case that the voltage of the positive-side input electrode 18subsequently changes and becomes lower than the voltage of thenegative-side input electrode 20, the forward and reverse iron cores 10f and 10 r undergo magnetic flux changes which are opposite to those inthe case described above. The directions of the voltages generated inthe forward and reverse secondary coils 14 f and 14 r are opposite tothose in the case described above. A reverse voltage is applied to thefirst rectifying element 22, and a forward voltage is applied to thesecond rectifying element 24. The output voltage of the reversesecondary coil 14 r appears at the output electrode 26. The voltagegenerated is high due to the energy arising from the inducedelectromotive force and the previously stored energy. The forwardsecondary coil 14 f is isolated from the output electrode 26, and theenergy arising from the induced electromotive force is stored in theforward secondary coil 14 f.

In the transformer 2, a voltage is output to the output electrode 26from one of the forward and reverse secondary coils 14 f and 14 r, andenergy is stored in the other secondary coil 14. Voltage output to theoutput electrode 26 and energy storage are repeated in each of theforward and reverse secondary coils 14 f and 14 r. This circuit operatesas a single-phase full-wave rectifier.

The following will describe advantageous effects of the presentembodiment.

In the transformer 2 according to the present disclosure, the referenceelectrode 16 to which both the forward and reverse secondary coils 14 fand 14 r are connected is in the form of a plate. Heat generation islikely to occur in the forward and secondary coil 14 f, reversesecondary coil 14 r, forward iron core 10 f, and reverse iron core 10 rwhich undergo repeated energy storage and energy release. In theplate-shaped reference electrode 16, the cross-sectional areacontributing to thermal conduction and the surface area contributing toheat release can easily be increased. The reference electrode 16 makesan effective contribution to heat discharge from the iron cores 10 andsecondary coils 14. In the transformer 2, heat generation-inducedtemperature rise is reduced by a simple configuration.

In this embodiment, the reference electrode 16 is located between theforward and reverse iron cores 10 f and 10 r and between the forward andreverse secondary coils 14 f and 14 r. With the plate-shaped referenceelectrode 16 located between the forward and reverse iron cores 10 f and10 r and between the forward and reverse secondary coils 14 f and 14 r,heat generated in these cores and coils can be discharged effectively.In the transformer 2, heat generation-induced temperature rise isreduced by a simple configuration.

In this embodiment, the reference electrode 16 includes the projectingportion 88 projecting outward from the space between the forward andreverse iron cores 10 f and 10 r. The projecting portion 88 effectivelypromotes the heat release of the reference electrode 16. In thetransformer 2, heat generation-induced temperature rise is reduced by asimple configuration. Additionally, since the projecting portion 88 isspaced from the two iron cores 10 and two secondary coils 14, theprojecting portion 88 does not cause an increase in inductance of thereference electrode 16. In the reference electrode 16, a low inductanceis achieved.

In this embodiment, the base portion 78 of the reference electrode 16extends along the fourth pillar portions 42 and 56 of the forward andreverse iron cores 10 f and 10 r. The direction of the current flowingthrough the base portion 78 of the reference electrode 16 is parallel tothe directions of the magnetic fluxes of the forward and reverse ironcores 10 f and 10 r. The current of the reference electrode 16 does notaffect the magnetic fluxes of the forward and reverse iron cores 10 fand 10 r. In the transformer 2, a high power density is achieved.

In this embodiment, the forward iron core 10 f includes the cut portions48 in the first and second pillar portions 34 and 36. The cut portion 48of the first pillar portion 34 is covered by the first winding portion58 of the forward secondary coil 14 f. The cut portion 48 of the secondpillar portion 36 is covered by the second winding portion 60 of theforward secondary coil 14 f. Thus, leakage of the magnetic flux in theforward iron core 10 f is effectively prevented. Likewise, the cutportion of the first pillar portion 50 of the reverse iron core 10 r iscovered by the third winding portion 68 of the reverse secondary coil 14r. The cut portion of the second pillar portion 52 of the reverse ironcore 10 r is covered by the fourth winding portion 70 of the reversesecondary coil 14 r. Thus, leakage of the magnetic flux in the reverseiron core 10 r is effectively prevented. In the transformer 2, a highpower density is achieved.

In this embodiment, the connection portion 62 of the forward secondarycoil 14 f extends parallel to the third and fourth pillar portions 40and 42 of the forward iron core 10 f. The direction of the currentflowing through the connection portion 62 is parallel to the directionof the magnetic flux of the forward iron core 10 f. The current of theconnection portion 62 does not affect the magnetic flux of the forwardiron core 10 f. In the transformer 2, a high power density is achieved.

In this embodiment, the connection portion 72 of the reverse secondarycoil 14 r extends parallel to the third and fourth pillars portions 54and 56 of the reverse iron core 10 r. The direction of the currentflowing through the connection portion 72 is parallel to the directionof the magnetic flux of the reverse iron core 10 r. The current of theconnection portion 72 does not affect the magnetic flux of the reverseiron core 10 r. In the transformer 2, a high power density is achieved.

In this embodiment, the first primary coil 12 a is wound outside thefirst winding portion 58 over substantially the entire width of thefirst winding portion 58. The first primary coil 12 a is wound outsidethe third winding portion 68 over substantially the entire width of thethird winding portion 68. Thus, a high coefficient of coupling betweenthe first primary coil 12 a and the forward and reverse secondary coils14 f and 14 r is achieved. In the transformer 2, a high power density isachieved.

In this embodiment, the second primary coil 12 b is wound outside thesecond winding portion 60 over substantially the entire width of thesecond winding portion 60. The second primary coil 12 b is wound outsidethe fourth winding portion 70 over substantially the entire width of thefourth winding portion 70. Thus, a high coefficient of coupling betweenthe second primary coil 12 b and the forward and reverse secondary coils14 f and 14 r is achieved. In the transformer 2, a high power density isachieved.

The forward iron core 10 f and the forward secondary coil 14 f arepreferably in indirect contact with each other, with a thermallyconductive insulator interposed between the forward iron core 10 f andthe forward secondary coil 14 f. In this case, heat generated in theforward iron core 10 f can be effectively discharged through the forwardsecondary coil 14 f. The reverse iron core 10 r and the reversesecondary coil 14 r are preferably in indirect contact with each other,with a thermally conductive insulator interposed between the reverseiron core 10 r and the reverse secondary coil 14 r. In this case, heatgenerated in the reverse iron core 10 r can be effectively dischargedthrough the reverse secondary coil 14 r. In the transformer 2, heatgeneration-induced temperature rise is reduced by a simpleconfiguration.

In this embodiment, each of the top and bottom covers 4 and 6 is made ofa thermally conductive material. The top and bottom covers 4 and 6effectively discharge heat transferred from the iron cores 10 andsecondary coils 14. Further, there are the joints 8 connecting the topand bottom covers 4 and 6. The joints 8 are made of a thermallyconductive material. The joints 8 make an effective contribution to heatdischarge. In the transformer 2, heat generation-induced temperaturerise is reduced by a simple configuration.

At least one of the top cover 4, the bottom cover 6, and the joints 8preferably contains a cooling liquid therein. In this case, heat isdischarged more effectively. In the transformer 2, heatgeneration-induced temperature rise is reduced by a simpleconfiguration.

In this embodiment, when viewed in plan, the forward and reverse ironcores 10 f and 10 r are arranged side by side and parallel to eachother, the first and third winding portions 58 and 68 are arranged sideby side, and the second and fourth winding portions 60 and 70 arearranged side by side. Thus, the first primary coil 12 a covering thefirst and third winding portions 58 and 68 can be small in size. Thesecond primary coil 12 b covering the second and fourth winding portions60 and 70 can be small in size. In the transformer 2, downsizing isachieved.

In this embodiment, when viewed in plan, the forward and reversesecondary coils 14 f and 14 r are symmetrical in shape about a lineextending in the front-back direction and bisecting the distance betweenthe forward and reverse secondary coils 14 f and 14 r. Thus, the outputvoltages from the forward and reverse secondary coils 14 f and 14 r havewaveforms precisely inverse to each other. Further, in the transformer2, as shown in FIG. 2, the assembly of the forward iron core 10 f,reverse iron core 10 r, first primary coil 12 a, second primary coil 12b, forward secondary coil 14 f, and reverse secondary coil 14 r isbilaterally symmetrical in shape when viewed in plan. Thus, the outputvoltages from the forward and reverse secondary coils 14 f and 14 r havewaveforms more precisely inverse to each other. In the transformer 2,precise full-wave rectification can be achieved.

In the embodiment described above, the pair of forward iron core 10 fand forward secondary coil 14 f and the pair of reverse iron core 10 rand reverse secondary coil 14 r are arranged side by side when viewed inplan. The pair of forward iron core 10 f and forward secondary coil 14 fand the pair of reverse iron core 10 r and reverse secondary coil 14 rneed not be arranged side by side. For example, these pairs may bearranged in such a manner that the forward and reverse iron cores 10 fand 10 r are perpendicular to each other. In the transformer 2, thepositions of the pair of forward iron core 10 f and forward secondarycoil 14 f and the pair of reverse iron core 10 r and reverse secondarycoil 14 r can be defined so that the pairs form a shape suitable for theplace where the transformer 2 is to be installed.

FIG. 11 is a plan view showing secondary coils 96 of a transformer 94according to another embodiment. As shown in FIG. 11, each of theforward and reverse secondary coils 96 f and 96 r includes a kink 98 ina connection portion 100. The forward and reverse secondary coils 96 fand 96 r are likely to generate heat because of high currents flowingthrough the coils 96 f and 96 r. The forward and reverse secondary coils96 f and 96 r could be deformed due to thermal expansion. Deformation ofthe forward or reverse secondary coil 96 f or 961 could lead to contactof the coil 96 f or 96 r with a neighboring component. In each secondarycoil 96 including the kink 98, the kink 98 is deformed due to thermalexpansion, and thus deformation of the rest of the coil 96 is reduced.The kink 98 is not limited to being included in the connection portion100. The kink 98 may be included in a portion other than the connectionportion 100.

FIG. 12 is a perspective view showing iron cores 112, primary coils 114,secondary coils 116, and reference electrodes 118 of a transformer 110according to yet another embodiment. Although not shown, the transformer110 further includes covers covering the cores, coils, and electrodes.In FIG. 12, the arrow X represents the frontward direction with respectto the transformer 110, and the opposite direction is the backwarddirection with respect to the transformer 110. The arrow Y representsthe rightward direction with respect to the transformer 110, and theopposite direction is the leftward direction with respect to thetransformer 110. The arrow Z represents the upward direction withrespect to the transformer 110, and the opposite direction is thedownward direction with respect to the transformer 110. FIG. 13 is aplan view showing the secondary coils 116 and reference electrodes 118of FIG. 12.

As shown in FIGS. 12 and 13, the transformer 110 includes two iron cores112, two secondary coils 116, two primary coils 114, and two referenceelectrodes 118. The iron cores 112 and primary coils 114 are the same asthe iron cores 10 and primary coils 12 of the transformer 2 of FIG. 1.One of the two secondary coils 116 is referred to as “forward secondarycoil 116 f”, and the other secondary coil 116 is referred to as “reversesecondary coil 116 r”. The reference electrode 118 connected to theforward secondary coil 116 f is referred to as “forward referenceelectrode 118 f”, and the reference electrode 118 connected to thereverse secondary coil 116 r is referred to as “reverse referenceelectrode 118 r”.

As shown in FIG. 13, the forward secondary coil 116 f includes a firstwinding portion 120, a second winding portion 122, a connection portion124, a first terminal 126, and a second terminal 128. Each of the firstand second winding portions 120 and 122 is a wound conductor in the formof a plate. The first winding portion 120 is wound around a first pillarportion 130 of the forward iron core 112 f. Although not shown, thefirst winding portion 120 covers a cut portion of the first pillarportion 130. The second winding portion 122 is wound around a secondpillar portion 134 of the forward iron core 112 f. The second windingportion 122 covers a cut portion of the second pillar portion 134.

The connection portion 124 connects the first and second windingportions 120 and 122. The connection portion 124 extends parallel tothird and fourth pillar portions 136 and 138 of the forward iron core112 f. The connection portion 124 is in the form of a plate. The widthdirection of the connection portion 124 is the right-left direction (thedirection from the forward secondary coil 116 f to the reverse secondarycoil 116 r), and the connection portion 124 extends in the directionfrom the first winding portion 120 to the second winding portion 122.

The first terminal 126 is in the form of a plate. The first terminal 126projects ahead of the second winding portion 122. The second terminal128 is in the form of a plate. The second terminal 128 is locatedbetween the first and second winding portions 120 and 122. The secondterminal 128, first winding portion 120, connection portion 124, secondwinding portion 122, and first terminal 126 are connected in series inthis order.

As shown in FIG. 13, the reverse secondary coil 1161 includes a thirdwinding portion 140, a fourth winding portion 142, a connection portion144, a first terminal 146, and a second terminal 148. Each of the thirdand fourth winding portions 140 and 142 is a wound conductor in the formof a plate. As shown in FIG. 12, the third winding portion 140 is woundaround a first pillar portion 150 of the reverse iron core 112 r.Although not shown, the third winding portion 140 covers a cut portionof the first pillar portion 150. The fourth winding portion 142 is woundaround a second pillar portion 152 of the reverse iron core 112 r. Thefourth winding portion 142 covers a cut portion of the second pillarportion 152.

The connection portion 144 connects the third and fourth windingportions 140 and 142. The connection portion 144 extends parallel tothird and fourth pillar portions 154 and 156 of the reverse iron core112 r. The connection portion 144 is in the form of a plate. The widthdirection of the connection portion 144 is the right-left direction (thedirection from the forward secondary coil 116 f to the reverse secondarycoil 116 r), and the connection portion 144 extends in the directionfrom the third winding portion 140 to the fourth winding portion 142.

The first terminal 146 is in the form of a plate. The first terminal 146projects ahead of the fourth winding portion 142. The second terminal148 is in the form of a plate. The second terminal 148 is locatedbetween the third and fourth winding portions 140 and 142. The secondterminal 148, third winding portion 140, connection portion 144, fourthwinding portion 142, and first terminal 146 are connected in series inthis order.

The forward reference electrode 118 f is located between the first andsecond winding portions 120 and 122 as shown in FIG. 13. The forwardreference electrode 118 f projects from the space between the first andsecond winding portions 120 and 122 toward the outside of thetransformer 110. The forward reference electrode 118 f is in the form ofa plate. The forward reference electrode 118 f is in contact with thesecond terminal 128 of the forward secondary coil 116 f. In thisembodiment, the forward reference electrode 118 f is integral with thesecond terminal 128.

The reverse reference electrode 118 r is located between the third andfourth winding portions 140 and 142 as shown in FIG. 13. The reversereference electrode 1181 projects from the space between the third andfourth winding portions 140 and 142 toward the outside of thetransformer 110. The reverse reference electrode 118 r is in the form ofa plate. The reverse reference electrode 118 r is in contact with thesecond terminal 148 of the reverse secondary coil 116 r. In thisembodiment, the reverse reference electrode 118 r is integral with thesecond terminal 148.

As shown in FIGS. 12 and 13, the transformer 110 includes the tworeference electrodes 118. Both of the two reference electrodes 118 areconnected to the same terminal of an external load. The forward andreverse reference electrodes 118 f and 118 r are connected to each otheroutside the transformer 110. When the transformer 110 is in use, thecircuit of the transformer 110 is equivalent to the circuit diagramshown in FIG. 3.

In the transformer 110 according to the present disclosure, the forwardreference electrode 118 f to which the forward secondary coil 116 f isconnected is in the form of a plate. Further, the reverse referenceelectrode 118 r to which the reverse secondary coil 116 r is connectedis also in the form of a plate. In the plate-shaped reference electrodes118, the cross-sectional areas contributing to thermal conduction andthe surface areas contributing to heat release can easily be increased.The reference electrodes 118 make an effective contribution to heatdischarge from the iron cores 112 and secondary coils 116. In thetransformer 110, heat generation-induced temperature rise is reduced bya simple configuration.

In this embodiment, the transformer 110 includes the forward and reversereference electrodes 118 f and 118 r. These electrodes are not connectedinside the transformer 110. For example, in the case where there is alarge reference electrode (ground) such as a housing of a device, theforward and reverse reference electrodes 118 f and 118 r can easily beconnected to the large reference electrode. Since the forward andreverse reference electrodes 118 f and 118 r are not connected insidethe transformer 110, the structure of the transformer 110 is simple. Thetransformer 110 can be small in size.

In this embodiment, the connection portion 124 of the forward secondarycoil 116 f is in the form of a plate. The connection portion 124contributes to heat discharge. The width direction of the connectionportion 124 is the direction from the forward secondary coil 116 f tothe reverse secondary coil 116 r. The width of the connection portion124 can be adjusted by adjusting the distance between the forward andreverse secondary coils 116 f and 116 r. In the transformer 110, theheat discharge performance can easily be adjusted. In the transformer110, heat generation-induced temperature rise is reduced by a simpleconfiguration.

In this embodiment, the connection portion 144 of the reverse secondarycoil 116 r is in the form of a plate. The connection portion 144contributes to heat discharge. The width direction of the connectionportion 144 is the direction from the forward secondary coil 116 f tothe reverse secondary coil 116 r. The width of the connection portion144 can be adjusted by adjusting the distance between the forward andreverse secondary coils 116 f and 116 r. In the transformer 110, theheat discharge performance can easily be adjusted. In the transformer110, heat generation-induced temperature rise is reduced by a simpleconfiguration.

As described above, the present disclosure can provide a current-doublertransformer in which heat generation-induced temperature rise is reducedby a simple configuration. This clearly demonstrates the superiority ofthe transformer.

The transformer as described above is applicable to various kinds ofelectric devices such as AC-DC converters and DC-DC converters.

[Disclosed Items]

The following items are directed to preferred embodiments.

[Item 1]

A transformer including:

a positive-side input electrode;

a negative-side input electrode;

an output electrode;

a single reference electrode or a plurality of reference electrodes;

a forward iron core;

a reverse iron core;

a first primary coil;

a second primary coil;

a forward secondary coil;

a reverse secondary coil;

a first rectifying element; and

a second rectifying element, wherein:

a first terminal of the first primary coil is connected to thepositive-side input electrode, and a second terminal of the firstprimary coil is connected to the negative-side input electrode;

a first terminal of the second primary coil is connected to thepositive-side input electrode, and a second terminal of the secondprimary coil is connected to the negative-side input electrode;

a first terminal of the forward secondary coil is connected to a firstterminal of the first rectifying element, and a second terminal of theforward secondary coil is connected to the single reference electrode orany of the plurality of reference electrodes;

a first terminal of the reverse secondary coil is connected to a firstterminal of the second rectifying element, and a second terminal of thereverse secondary coil is connected to the single reference electrode orany of the plurality of reference electrodes;

second terminals of the first and second rectifying elements areconnected to the output electrode;

the forward secondary coil includes first and second winding portionsboth of which are wound around the forward iron core;

the reverse secondary coil includes third and fourth winding portionsboth of which are wound around the reverse iron core;

the first primary coil is formed around the first and third windingportions;

the second primary coil is formed around the second and fourth windingportions;

the single reference electrode or each of the plurality of referenceelectrodes is in the form of a plate;

winding directions of the first and second primary coils and the first,second, third, and fourth winding portions are defined so that voltagesinverse to each other are generated at the respective first terminals ofthe forward and reverse secondary coils upon a change in a voltageapplied between the positive-side and negative-side input electrodes;and

the voltage of the first terminal of the forward or reverse secondarycoil is output through the output electrode by bringing one of the firstand second rectifying elements into a conducting state while bringingthe other of the first and second rectifying elements into anon-conducting state.

[Item 2]

The transformer according to Item 1, wherein:

the forward iron core includes a cut portion; and

the first or second winding portion is wound around the forward ironcore to cover the cut portion.

[Item 3]

The transformer according to Item 1, wherein:

the forward iron core is in the form of a frame having outer and innerperipheral surfaces with rectangular contours and includes opposingfirst and second pillar portions extending parallel to each other andopposing third and fourth pillar portions extending parallel to eachother;

the first winding portion is wound around the first pillar portion; and

the second winding portion is wound around the second pillar portion.

[Item 4]

The transformer according to Item 3, wherein:

the forward secondary coil further includes a connection portionconnecting the first and second winding portions; and

the connection portion extends parallel to the third and fourth pillarportions.

[Item 5]

The transformer according to Item 4, wherein the connection portion isin the form of a plate.

[Item 6]

The transformer according to Item 3, including the single referenceelectrode, wherein:

the single reference electrode includes a base portion, a firstextraction portion connected to the second terminal of the forwardsecondary coil, and a second extraction portion connected to the secondterminal of the reverse secondary coil; and

the base portion extends along the fourth pillar portion.

[Item 7]

The transformer according to Item 1, including the single referenceelectrode, wherein the single reference electrode is located between theforward and reverse iron cores and between the forward and reversesecondary coils when viewed in plan.

[Item 8]

The transformer according to Item 7, wherein the reference electrodeincludes a projecting portion projecting outward from a space betweenthe forward and reverse iron cores.

[Item 9]

The transformer according to Item 1, including a forward referenceelectrode and a reverse reference electrode, wherein:

the second terminal of the forward secondary coil is connected to theforward reference electrode;

the second terminal of the reverse secondary coil is connected to thereverse reference electrode;

the forward reference electrode projects outward from a space betweenthe first and second winding portions; and

the reverse reference electrode projects outward from a space betweenthe third and fourth winding portions.

[Item 10]

The transformer according to Item 1, wherein the forward secondary coilincludes a kink.

[Item 11]

The transformer according to Item 1, wherein:

each of the first and second winding portions is a wound conductor inthe form of a plate;

the first primary coil is wound outside the first winding portion oversubstantially the entire width of the first winding portion; and

the second primary coil is wound outside the second winding portion oversubstantially the entire width of the second winding portion.

[Item 12]

The transformer according to Item 1, wherein the forward iron core andthe forward secondary coil are in indirect contact with each other, witha thermally conductive insulator interposed between the forward ironcore and the forward secondary coil.

[Item 13]

The transformer according to Item 1, wherein when viewed in plan, theforward and reverse iron cores are arranged side by side and parallel toeach other, the first and third winding portions are arranged side byside, and the second and fourth winding portions are arranged side byside.

[Item 14]

The transformer according to Item 13, wherein the forward and reversesecondary coils are symmetrical in shape when viewed in plan.

[Item 15]

The transformer according to Item 1, further including:

a top cover made of a thermally conductive material;

a bottom cover made of a thermally conductive material; and

a joint made of a thermally conductive material, wherein:

the forward and reverse iron cores, the first and second primary coils,and the forward and reverse secondary coils are located between the topand bottom covers; and

the top and bottom covers are connected by the joint.

[Item 16]

The transformer according to Item 15, wherein at least one of the topcover, the bottom cover, and the joint contains a cooling liquidtherein.

[Item 17]

The transformer according to Item 15, wherein the bottom cover iselectrically conductive and connected to the reference electrode.

What is claimed is:
 1. A transformer comprising: a positive-side inputelectrode; a negative-side input electrode; an output electrode; asingle reference electrode or a plurality of reference electrodes; aforward iron core; a reverse iron core; a first primary coil; a secondprimary coil; a forward secondary coil; a reverse secondary coil; afirst rectifying element; and a second rectifying element, wherein: afirst terminal of the first primary coil is connected to thepositive-side input electrode, and a second terminal of the firstprimary coil is connected to the negative-side input electrode; a firstterminal of the second primary coil is connected to the positive-sideinput electrode, and a second terminal of the second primary coil isconnected to the negative-side input electrode; a first terminal of theforward secondary coil is connected to a first terminal of the firstrectifying element, and a second terminal of the forward secondary coilis connected to the single reference electrode or any of the pluralityof reference electrodes; a first terminal of the reverse secondary coilis connected to a first terminal of the second rectifying element, and asecond terminal of the reverse secondary coil is connected to the singlereference electrode or any of the plurality of reference electrodes;second terminals of the first and second rectifying elements areconnected to the output electrode; the forward secondary coil includesfirst and second winding portions both of which are wound around theforward iron core; the reverse secondary coil includes third and fourthwinding portions both of which are wound around the reverse iron core;the first primary coil is formed around the first and third windingportions; the second primary coil is formed around the second and fourthwinding portions; the single reference electrode or each of theplurality of reference electrodes is in the form of a plate; windingdirections of the first and second primary coils and the first, second,third, and fourth winding portions are defined so that voltages inverseto each other are generated at the respective first terminals of theforward and reverse secondary coils upon a change in a voltage appliedbetween the positive-side and negative-side input electrodes; and thevoltage of the first terminal of the forward or reverse secondary coilis output through the output electrode by bringing one of the first andsecond rectifying elements into a conducting state while bringing theother of the first and second rectifying elements into a non-conductingstate.
 2. The transformer according to claim 1, wherein: the forwardiron core includes a cut portion; and the first or second windingportion is wound around the forward iron core to cover the cut portion.3. The transformer according to claim 1, wherein: the forward iron coreis in the form of a frame having outer and inner peripheral surfaceswith rectangular contours and includes opposing first and second pillarportions extending parallel to each other and opposing third and fourthpillar portions extending parallel to each other; the first windingportion is wound around the first pillar portion; and the second windingportion is wound around the second pillar portion.
 4. The transformeraccording to claim 3, wherein: the forward secondary coil furtherincludes a connection portion connecting the first and second windingportions; and the connection portion extends parallel to the third andfourth pillar portions.
 5. The transformer according to claim 4, whereinthe connection portion is in the form of a plate.
 6. The transformeraccording to claim 3, comprising the single reference electrode,wherein: the single reference electrode includes a base portion, a firstextraction portion connected to the second terminal of the forwardsecondary coil, and a second extraction portion connected to the secondterminal of the reverse secondary coil; and the base portion extendsalong the fourth pillar portion.
 7. The transformer according to claim1, comprising the single reference electrode, wherein the singlereference electrode is located between the forward and reverse ironcores and between the forward and reverse secondary coils when viewed inplan.
 8. The transformer according to claim 7, wherein the referenceelectrode includes a projecting portion projecting outward from a spacebetween the forward and reverse iron cores.
 9. The transformer accordingto claim 1, comprising a forward reference electrode and a reversereference electrode, wherein: the second terminal of the forwardsecondary coil is connected to the forward reference electrode; thesecond terminal of the reverse secondary coil is connected to thereverse reference electrode; the forward reference electrode projectsoutward from a space between the first and second winding portions; andthe reverse reference electrode projects outward from a space betweenthe third and fourth winding portions.
 10. The transformer according toclaim 1, wherein the forward secondary coil includes a kink.
 11. Thetransformer according to claim 1, wherein: each of the first and secondwinding portions is a wound conductor in the form of a plate; the firstprimary coil is wound outside the first winding portion oversubstantially the entire width of the first winding portion; and thesecond primary coil is wound outside the second winding portion oversubstantially the entire width of the second winding portion.
 12. Thetransformer according to claim 1, wherein the forward iron core and theforward secondary coil are in indirect contact with each other, with athermally conductive insulator interposed between the forward iron coreand the forward secondary coil.
 13. The transformer according to claim1, wherein when viewed in plan, the forward and reverse iron cores arearranged side by side and parallel to each other, the first and thirdwinding portions are arranged side by side, and the second and fourthwinding portions are arranged side by side.
 14. The transformeraccording to claim 13, wherein the forward and reverse secondary coilsare symmetrical in shape when viewed in plan.
 15. The transformeraccording to claim 1, further comprising: a top cover made of athermally conductive material; a bottom cover made of a thermallyconductive material; and a joint made of a thermally conductivematerial, wherein: the forward and reverse iron cores, the first andsecond primary coils, and the forward and reverse secondary coils arelocated between the top and bottom covers; and the top and bottom coversare connected by the joint.
 16. The transformer according to claim 15,wherein at least one of the top cover, the bottom cover, and the jointcontains a cooling liquid therein.
 17. The transformer according toclaim 15, wherein the bottom cover is electrically conductive andconnected to the reference electrode.